Sennheiser HD238: Brief Review and Modding

Just recently, I was in the market for a portable headphone so decided to try out the Sennheiser HD238 which I was able to get brand new for $75.

Anyways, straight to the acoustics review:

My initial impressions of the headphone was that it was terrible. Simply terrible. The bass was uneven and muddy. The highs are almost non-existent. Both the bass and mid-range were distorted at high volume....well actually, it was strangely and annoyingly distorted throughout, didn't had to be at high volume. The vocals were horrible; they were unclear and soundstage was one of the worst I have ever heard.

However, after about 100 hours, the acoustics improved dramatically. The highs began to clear up and most of the distortion ceased. The bass also sharpened and overall, the HD238 became more balanced with better clarity.

I do should point out though; this was tested using only the digital amplifier on the Ipod Classic. But when I got my Corda Headsix, the acoustics improved once again. Despite that, the final review for the Sennheiser HD238 powered by the Corda Headsix and with lossless audio files on an Ipod Classic follows this set of pictures:

STOCK:
Strong response for bass but slightly muddy. However, bass is not very accurate; despite that, the mid-range great due to the range balance; also there is an extremely light distortion at high volume; and soundstage is just terrible and the high frequency sounds like its played through a brick wall.

So it begins my quest to improve the sound of the HD238:

Disassembling the headphone:

Note; the original cup foam has been taken out. In the next following set of pictures, I test out different materials as the back-material for the drivers of the headphone; hoping that finding the right material will improve the overall sound.

Bandage Roll:
More impact on bass. slightly improved bass in terms of accuracy, soundstage still bad, vocals/high frequency has no change, distortion at high volume still exist, the mid-range doesn't seem to change.

Cotton Balls:
Bass is much more impactful. slightly more accurate and with less muddiness. vocals sound closer and more detailed and so the soundstage has improved. the mid-range seems to have no change, distortion at high volume still exist.

Medium Felt(Yellow):
Bass weakens; any difference in terms of accuracy and muddiness is unclear. the detail for vocals is an improvement over stock but not better than cotton. the mid-range seems to also have weakened. however, the distortion also seem to have disappeared. In essence, I feel this is more controlled than the bandage/cotton, more neutral in other words.

Thick Felt (Black)
The bass sounds somewhat close to the medium felt; however, its accurate and very well controlled. the best bass so far in the test. The vocals are more detailed and the soundstage has improved overall. Also, compared to the other materials so far, the sound here sounds the most forward, sounds great when playing rock.

Aluminum Foil:
Holy crap! A whole world of difference! Firstly, the highs have improved dramatically; much more detailed and forward but overall very very very balance. when playing rock, this was the most enjoyable of all the materials because of it's forwardness. seems like it gets you up and close to the singer. On a particular mention: around 3:40 of Gypsy, all of the other materials sound like the main solo guitar is slightly far away where the aluminum foil sound like its right in front of you, very forward like I was saying. Crystal clarity without losing focus on the bass and
mid-range....overall, the highs are extremely enjoyable.

Secondly, the bass's accuracy has improved significantly, much more controlled without any distortion at high volume. When playing Layla, the other materials didn't really didn't really allow the bass to shine whereas the aluminum foil; it was extremely noticeable...also during the vocals of the song, you lose focus on the bass with the other material but with the foil, the bass is even and can be heard/felt throughout the whole song.

Significant improvement; especially one of my goals for modding was to get better highs and clarity because I felt the stock was way too muddy and distorted. Definitely made the HD238 more fun to listen to.

Aluminum Foil Throughout The Whole Cup:
Hmm...this one is interesting. first of all, it's quite bright .... good and bad, good because the highs are better in detail compared to the first aluminum foil. when focusing on certain instruments, this setup really shines. And it
actually sounds much more forward than the first aluminum setup. But bad because it can become too bright and it develops harshness. Overall I would say that the aluminum 2 is an slight improvement over the aluminum 1 in the highs, simply because of the detail but can be rather harsh.

Secondly, I can't say that despite having better highs that I enjoy this setup; the bass's magnitude has dropped tremendously, in essence, the bass is hardly impactful even compared to stock. This definitely kills the fun whenlistening to rock or bassy music.

Thirdly, where has the mid-range gone?

Overall, this setup is too bright....you know, it kind of sounds like my k701 even the detail is similar....well slightly, k701 still has better detail and sound more balanced.

Aluminum Foil Throughout The Whole Cup With All 3 Types of Felt:
The intention with this one was to attempt to improve the bass while keeping the brightness. It worked but the bass still wasn't close enough to the detail and power of the first aluminum setup. Still a little too bright, I decide I won't bother with the
aluminum foil throughout the whole cup anymore.

So finally, this makes me think about how I can approach my goal which is to get the most out of the highs while improving the bass to make it more balanced and controlled. I determined that I should use the first setup of the aluminum foil to achieve the great highs and balanced bass. In addition to that, I should use the felts to smooth out the bass and make it more accurate. Another advantage to using the felt is that the mid-range and soundstage will improve as the individual felt tests show.

Anyways, this's the best sounding setup I found: in order of placement in the cup:

In comparison to stock, this is a tremendous improvement. The whole range has become more accurate and detailed. The bass is impactful and shows smoothness and balance and the highs demonstrate great detail and sharpness in vocals and in instruments. The soundstage/forwardness makes the listening experience more enjoyable. Overall, I am extremely impressed with how this turned out.

Wow, great job on the HD238 mod. Mine has the outer black foams taken off, where clarity and soundstage improved slightly even without the Astroid mod (taking off the black inner f9oam in the earpads). So, having tin foil improves the sound significantly... I have yet to try that.

What does this mod do to sound traveling outside the phones?? Sounds as if you made these a closed headphone vs the open set which they were originally..
funny but I wanted these but being a open headphone was a drawback(I listen on the loud side with people in the room. Sounds like you might have modded these to suit me

What does this mod do to sound traveling outside the phones?? Sounds as if you made these a closed headphone vs the open set which they were originally..
funny but I wanted these but being a open headphone was a drawback(I listen on the loud side with people in the room. Sounds like you might have modded these to suit me

Somewhat yes....but I noticed that the more "closed" it becomes, the more bass and mids are lost while the highs became more detailed. Obviously, that wasn't what I was aiming for...so that's why I wanted something in between. Great Bass and Mids while still retaining great highs....

Thanks for the write up. I just picked up a pair at Best Buy as they've been marked down to $55 USD. Been eyeing them for awhile but thought the $100+ MSRP was a bit much. At the current price, a little modding might be in the cards. Certainly not losing much $$$ if I screw something up.

hey every one this is my first post!!! yay!! just wana say thanks for this write up.. i have the HD238s they are 50% broken in .. i got them at best buy for $60 to use with my iphone... i did the tin foil mod but i replaced the original foam over the tinfoil and got great results all brightness was cured and the sound stage is 25% higher..

I rate these cans used with iphone a 8.5 out of 10.. clarity transparency are nice base is tight but volume is not loud enough so impact is lacking maybe cause they are not fully broken in.. the sound is real and natureal.. no artificially boosting is frequenies.. so if you play a crappy recording or lossy mp3 etc it will sound crappy but if you play great material it will shine..

hey every one this is my first post!!! yay!! just wana say thanks for this write up.. ji have the HD238s they are 50% broken in .. i got them at best buy for $60 to use with my iphone... i did the tin foil mod but i replaced the original foam over the tinfoil and got great results..

Glad you got great results.

Today, I give my buddy a try at my modded HD238 and he was absolutely amazed at how great it sounds modded.

What does this mod do to sound traveling outside the phones?? Sounds as if you made these a closed headphone vs the open set which they were originally..
funny but I wanted these but being a open headphone was a drawback(I listen on the loud side with people in the room. Sounds like you might have modded these to suit me

Mine still leak sound outside but not as much but remember that the ear cushions are also "open" so you would need to replace or mod those to creat more isolation..

Today, I give my buddy a try at my modded HD238 and he was absolutely amazed at how great it sounds modded.

I'll looking forward to recabling them too.

ok so update i was noticing some note compression in my modded 238s...! i so i decided i wanted more air flow off the diaphragms so i took out the black center foam from the ear cushions (this increased comfort too!!) and re worked the foil mod so that the foil is very firmly secured to the black metal grill at the back of each enclosure to reduce resonance that saps precious energy.. (I also removed the factory foam that i had previously left in)

i used a pen to mold the foil to each hole in the metal and used small pieces or electric tape to secure the foil from moving!!! SO NOW THE SOUND IS DRAMATICALLY IMPROVED!!! WOW... the sound is fuller richer and super smooth!!! the best part is they play 20% louder now also..

To all doing this foil mod as i did make sure to mold the foils to the grills and secure the foil in place very well that is the secrete that allowed me to strike gold!!!

Nice work! Wouldn't you feel that a re-cable is kind of an overkill for this pair?

Not really. When I re-cabled my A700, there were dramatic sonic differences; I figured that the HD238 still has a lot of potential so I should attempt to re-cable them. Also, I feel that the stock plug is way too cheap, that's why I just bought the XLO 3.5mm plug to re-cable them.

ok so update i was noticing some note compression in my modded 238s...! i so i decided i wanted more air flow off the diaphragms so i took out the black center foam from the ear cushions (this increased comfort too!!) and re worked the foil mod so that the foil is very firmly secured to the black metal grill at the back of each enclosure to reduce resonance that saps precious energy.. (I also removed the factory foam that i had previously left in)

i used a pen to mold the foil to each hole in the metal and used small pieces or electric tape to secure the foil from moving!!! SO NOW THE SOUND IS DRAMATICALLY IMPROVED!!! WOW... the sound is fuller richer and super smooth!!! the best part is they play 20% louder now also..

To all doing this foil mod as i did make sure to mold the foils to the grills and secure the foil in place very well that is the secrete that allowed me to strike gold!!!

Not really. When I re-cabled my A700, there were dramatic sonic differences; I figured that the HD238 still has a lot of potential so I should attempt to re-cable them. Also, I feel that the stock plug is way too cheap, that's why I just bought the XLO 3.5mm plug to re-cable them.

Mine are now completely broken in now and i have to say teat once modded these cans are top shelf.. They are on clearance now at most sellers so you can get them for as low as $45!! But I will only recommend if your are brave enough to mod..!